1. Field of the Invention
This invention relates generally to woven webbing for use in restraint systems, and more particularly to, woven webbing having shock absorption characteristics.
2. Related Art
Woven webbings have been used as straps and slings for various restraint systems such as seat belts for automobiles, harnesses for industrial applications, or tie-downs for securing or supporting various objects. The woven strap is typically formed by weaving a tube from warp yarns and weft yarns, and then flattening the tube to form a two layer woven strap. The two layers are woven together by binder yarns. Stuffer yarns may also be used and are sandwiched between the two layers for increasing the overall strength and/or thickness of the woven strap. Although the strap is useful for securing a variety of objects, it has limited stretchability.
In some situations, it is desirable to provide a strap that includes shock absorbing characteristics. In one typical construction, the strap is alternately folded upon itself and sewn through the folds with a thread that has less strength then that of the woven strap. In a situation where a great amount of force is exerted on the strap, such as may be the case with a falling object or person, or during a rapid deceleration of an automobile for example, the alternating folds of the strap separate due to tearing of the stitching between the alternating folds. Energy is absorbed by the tearing of the stitching, and therefore less energy is transmitted to either the object or the person.
In another typical construction, the strap, which is in the form of a tube, is partially axially collapsed. An elastic member is placed within the collapsed tube and anchored to the tube at its ends. Large forces are absorbed by the expansion of the elastic member within the tube until the length of the elastic member increases to the uncollapsed length of the tube. At that point, the tube prevents continued expansion of the elastic member.
In both of the previously described constructions, secondary operations are required during manufacture of the strap to produce the shock absorbing characteristics. Such secondary operations tend to be more costly. Further, the integrity of the shock absorbing characteristics is limited by the integrity of the labor intensive post-weaving operations of either stitching the alternating folds or anchoring the elastic member at its ends.